The invention relates to corneal reshaping and more particularly to multipolar electrodes utilizing radio-frequency electrical current to heat and thereby induce reshaping of the cornea in mammals.
Extreme cases of refractive error, such as those caused by keratoconus, are frequently not correctable by the addition of external refraction. Corneal transplant is the usual remedy. Recent alternatives have been suggested which include modification of the corneal shape by thermal methods which rely upon dramatic shrinkage of corneal collagen in about 55.degree. to 65.degree. Centrigrade (C.) range. The use of these thermal methods has been limited by damage to the epithelium and Bowman's membrane, and by the temporary nature of the change affected. Each of these problems appear to be related to the thermal dose profile within the cornea which is generated by conventional conductive heating apparatus. Temperatures reached in the epithelium are relatively high while temperatures reached in the deeper stromal collagen are below the critical shrinkage temperature needed. A wide variability in treatment results exists which is probably caused by unintentional variation in individual techniques in administering thermal treatments, particularly in the length of time that heat is applied.
A corneal shaping electrode is disclosed in U.S. Pat. No. 4,326,529 issued Apr. 27, 1982 by James D. Doss and Richard L. Hutson, and is also described in "A Technique for the Selective Heating of Corneal Stroma," Contact and Intraocular Lens Medical Jrl. 6, No. 1, pp. 13-17 (January-March 1980). The monopolar electrode therein has been utilized on several mammals satisfactorily. The instant invention improves upon the monpolar electrode disclosed in U.S. Pat. No. 4,326,529. For example, no remote electrode is utilized. This means a patient's hair and skin at the rear of his head need not be wetted and cleansed because no remote electrode need be applied thereto. Too, because there is no remote electrode attached to the rear of the head, much less current need flow through the patient's brain and optic nerve. In addition, inherently high electric fields at the edge of the treatment region of the corneal shaping electrode of U.S. Pat. No. 4,326,529 are avoided by utilizing the present invention. Further, in practicing the instant invention, high current density and high coolant velocity are disposed in the same location on the corneal surface, providing highly effective removal of superficial heat.
In the monopolar probe of U.S. Pat. No. 4,326,529 electric current flows away from the probe in a direction that is approximately perpendicular to the surface of the cornea. In the present invention, current flows substantially parallel to the corneal surface between at least two electrode tips although there is a significant perpendicular component electric current immediately under a metallic electrode.